An MEMS (Micro Electro Mechanical System) sensor is formed by combining micro mechanical device (an embedded sensor in a semiconductor chip, a valve, a gear, a reflector, and an actuator) and a computing circuit. The MEMS sensor varies own capacitance according to external environment.
And, a circuit for converting a capacitance-to-time deviation detects variations of the capacitance of the MEMS sensor and outputs a time signal that has a pulse width corresponding to the detected variations of the capacitance.
However, in a case of the conventional circuit for converting a capacitance-to-time deviation, when the variation of the capacitance of the MEMS sensor is very small, the pulse width of the time signal also becomes very narrow. That is, since the circuit for converting a capacitance-to-time deviation has low resolution, it is difficult for a circuit that uses the time signal output from the circuit for converting a capacitance-to-time deviation to perform an accurate operation.
In a conventional art, in order to solve the problem, there has been proposed a method of increasing a driving voltage of the circuit for converting a capacitance-to-time deviation so that a time signal has a relatively wider pulse width despite a small variation of the capacitance. However, the method needs a higher driving voltage then before. Therefore, the method cannot be used in a circuit having a micro size and low power consumption.